Government agencies often are rapped for being unresponsive when their work is criticized, but the Federal Trade Commission has shown that it takes such opinions seriously.

The agency sent warning letters to 21 “influencers”— online celebrities who tout products on Instagram and other platforms — advising them that they must disclose business ties, payments or other connections to the product or service being promoted.

Former Federal Trade Commission Chairwoman Edith Ramirez has joined Hogan Lovells as co-head of the firm’s antitrust, competition and economic regulation practice. She also plans to play an “active role” …